I am confused about completeness relations. I thought a completeness relation was something like:(adsbygoogle = window.adsbygoogle || []).push({});

[tex] I = \sum_{i = 1}^n |i><i| = \sum_{i=1}^n P_i [[/tex]

where P_i is the projection operator onto i. Now I saw this called a completeness relation as well:

[tex]\delta(x - x') = \sum_{n=0}^\infty \Psi_n(x) \Psi_n(x')[/tex]

How is that the same as my first equation? What is the difference between x and x'? The second equation can be found at http://en.wikipedia.org/wiki/Green's_function

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# Homework Help: Completeness relations confusion

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